This invention relates to electric submergible motors, particularly of the elongated, multi-section type for driving submergible centrifugal pumps, and is concerned with isolating bearing assemblies from axial loads.
In submergible motors of the type comprising a long stator and multiple rotor sections, bearing assemblies are provided between successive rotor sections. Each bearing assembly includes a stationary bearing ring and a coaxial rotatable bearing sleeve therein. Thrust washers are provided at opposite ends of the bearing assembly. The bearing sleeves and bearing rings cooperate to maintain proper air gaps between the rotor sections and the stator. The thrust washers and bearing sleeves also carry axial gravity loads from rotor section to rotor section. Conventionally, the lowermost rotor section carries the entire axial gravity load of all of the rotor sections and has its lower end supported on a thrust bearing.
The rotor sections are compelled to rotate with the rotor shaft but are capable of limited axial movement relative to the shaft. The gravity loads applied to the bearing sleeves by the rotor sections are increased by the difference in thermal expansion between the rotor sections and the rotor shaft. The total rotor weight load and additional thermal expansion load can crush thrust washers and buckle bearing sleeves. The bearing sleeves will then seize on the inside of the bearing rings, causing the bearing rings to spin with the rotor and to damage the stator. Any misalignment in assembly and any dimensional errors in this arrangement will be additive and will further decrease clearances and amplify the negative effects of thermal expansion.
It has heretofore been proposed to prevent the deformation of thrust washers by employing thrust washers that fit just over the opposite ends of the fixed bearing rings, and by employing rotatable bearing sleeves that are long enough to engage the successive rotor sections and to prevent the application of axial gravity loads to the thrust washers and the fixed bearing rings. See, for example, U.S. Pat. No. 4,453,099, issued June 5, 1984. However, it has been discovered that a problem remains in this arrangement in that thermal expansion of rotor sections may apply great enough axial loads to the rotating bearing sleeves to cause the bearing sleeves to buckle and to seize on the inside of the supposedly fixed bearing rings, forcing the bearing rings to spin with the rotor and to damage the stator.